1. Field of the Invention
This invention relates to a machine for comminuting waste material. In a particular embodiment it relates to a shredder-mulcher for comminuting garden waste material.
2. Description of the Prior Art
The comminuation of materials for industrial use or for the disposal of wastes has for many years presented a technological challenge, with respect to both efficient use of available motor power and production of a desired end product.
Hagerty, U.S. Pat. No. 332,796, discloses a bark cutting machine comprising a disc, which can rotate about a vertical axis, having non-radial slots through which cutting blades extend upwardly. A cover fits closely over the disc and blade assembly and the cover is fitted with a plurality of narrow openings over which are fitted narrow hoppers so that tree bark can be fitted edge-wise to the cutters. The hopper sides slope downwardly in the direction of rotation of the blades so that bark will be caught between the blades and the hopper sides and not rise out of place.
Everett, U.S. Pat. No. 2,181,397, discloses a dual purpose feed mill for cutting and grinding corn stalks. The feed mill contains an ensilage cutter, blades mounted on a disc rotating about a horizontal axis for cutting corn stalkes into short length, and a grinder, flails mounted on a common axis with the disc for grinding cut corn stalks, in a common housing but separated by an annular ring. The annular ring contains a valve means whereby cut corn stalks from the ensilage cutter can be fed to the grinder.
Dunbar, U.S. Pat. No. 2,566,721, discloses a rotary disc chipper having a cover plate provided with at least one rectangular feed opening; a pulp-receiving shoe having an inclined passage communicating with the feed opening; a horizontal rotor below the cover plate; and a plurality of straight-edged chipper knives mounted on said rotor adapted to sweep across the rectangular feed opening, each knife being located with reference to a quadrant so as to be substantially perpendicular to the leading radius of the quadrant and substantially parallel to the trailing radius of the quadrant, each knife being of a length sufficient to completely traverse the feed opening and securely hold a piece of wood being cut in an angle of the rectangular opening and in the pulp-receiving shoe. Preferably, the number of knives on the rotor is one less or more than the number of openings so that the several knives will be at different points of engagement with the pulp logs in the shoes and the torque upon the shaft incidental to cutting the logs will be substantially constant.
Shively, U.S. Pat. No. 2,665,852, discloses an ice chipping machine comprising a working chamber including a hopper adapted to contain ice; a rotary plate in the chamber, having a plurality of openings and a plurality of picks adjacent the openings, the picks being adapted to form chips from said ice and to deflect the chips through the openings. A central breaker comprising a hub equipped with outwardly extending hooked picks is secured centrally on top of the rotary plate. Chipped ice which falls through the rotary plate is discharged through a discharge outlet by a centrifugal ejector.
Wexell, U.S. Pat. No. 3,069,101, discloses a wood chipper comprising a chipper disc mounted for rotation on a horizontal axis; a housing surrounding the disc, the housing having an outlet for chipped material; a first feed spout disposed horizontally and communicating with said housing; and a second feed spout inclining downwardly toward the housing and communicating with the housing at a level above and at substantially the same radius with respect to the disc as the first spout.
Prohl, U.S. Pat. No. 3,448,932, discloses a waste disposal device for a variety of fruit and vegetable waste materials. The device includes a frame providing a support for a housing containing a cutting/grinding chamber; a hopper located above the chamber for receiving waste material to be fed to the chamber; a rotary cutter assembly mounted in the chamber on a shaft driven by a motor, the rotary cutter assembly having a feed plate with mulching knives mounted thereon; a stationary cutter bar assembly is mounted on the wall of the chamber and includes a blade or anvil which cooperates with a feed knife mounted on top of the rotary cutter assembly, the feed knife partially overlying a feed slot formed at the outer margin of the cutter assembly.
Salzmann, Jr., U.S. Pat. No. 3,559,705, discloses a reversible, symmetrical knife for a drum-type wood chipper.
Hamlin, U.S. Pat. No. 3,817,462, discloses a shredder comprising a chute for supplying the material to the shredding mechanism; a hopper positioned over the chute into which material to be shredded may be placed; an impeller and a rotatable blade mounted on a horizontal shaft; and flails carried by the impeller which drive material through spaced fingers carried on a housing surrounding the blade and impeller.
Smith, U.S. Pat. No. 3,861,602, discloses a brush chipper for reducing material such as limbs, branches, brush and the like to chips wherein a powered feed mechanism moves material in a longitudinal path to a rotary chipping mechanism having a chipping disc rotatable about a substantially horizontal axis. The chipping disc mounts a single, radial, chipping knife which is angularly disposed relative to the feed path to draw the material into the mechanism.
Svensson, U.S. Pat. No. 4,047,670, discloses a rotary cutting apparatus having reversible cutters or knife devices mounted on a rotary disc.
Fudman, U.S. Pat. No. 4,113,190, discloses a device for shaving ice comprising a hopper for holding a supply of ice; an agitator positioned below said hopper to agitate said ice; a comminution system coupled to said agitator containing ice shaving components; and at least one baffle positioned within the hopper and monolithic with said hopper to impede turning of the total ice mass.
Svensson, U.S. Pat. No. 4,155,384, discloses a disc-type wood chipper having cutting knives disposed non-radially on a chipper disc to cut a slab of wood from a log and having guide means with ridges over which the slab is caused to slide so that the slap disintegrates into wood chips of substantially uniform size.
Lapointe, U.S. Pat. No. 4,159,083, discloses a debris separating chipper wherein the housing is divided by a chipping disc into a front chamber and a chip chamber and wherein separate outlets are provided from the front chamber and from the chip chamber, respectively, for twigs and the like and for chips whereby separation of chips from debris is obtained.
Nonetheless, the disposal of waste materials by comminuation continues to represent a major problem. In recent years, with bans on residential brush burning and with many cities reluctant to haul and dump voluminous masses of garden waste, such as leaves, tree prunings, garden stalks and hedge trimmings, an increasing focus on the disposal of garden wastes has occurred. Fortunately, a strong interest in organic gardening has also developed. However, in order to utilize garden waste materials in the efficient production of compost or mulch these materials should be comminuted to reduce bulk and increase surface area for reaction with organisms aiding decomposition. Many attempts have been made to supply apparatus for this purpose.
Lindsley ("Chippers and Shredders Cut Your Junk Yard Down to Size", Popular Science, November 1973, pp. 116-119) gives an overview of various commercially available machines such as shredder-baggers, grinder-composters (Hammermill-type) and chipper-shredders. Shredder-baggers having shaft-mounted rotary blades swinging through breaker plates can only handle leaves and small twigs. Grinder-composters of the Hammermill-type utilize pivoted flails to chop up all garden waste except heavy brush and limbs. Chipper-shredders utilize jointer-like blades mounted on a rotating disc to cut logs up to three inches in diameter, while shredding blades projecting from the periphery of the disc can shred lighter materials and the cut log pieces.
British Pat. No. 725,839 discloses a machine for grinding and/or masticating vegetable materials comprising a container having a top feed opening and a bottom discharge opening, a motor-driven shaft journalled in top and bottom journals supported by the container and a plurality of circumferentially spaced knives on said shaft. Material to be cut is dropped in the top and shredded by said knives and ejected by said knives which also function as impellers. However, such a machine cannot handle logs or heavy branches lest the blades break or the branches become caught in the blades clogging the machine.
German Offenlegungsschrift No. 1,944,559 discloses a shredder for garden debris comprising a disc-like blade holder which rotates on a motor-driven shaft. A plurality of rectangular blades are pivotally mounted on the outer edge portion of the disc by bolts passing through the disc and one end of the rectangular blade. A housing covers the rotating disc and blades, the housing being fitted with a funnel-like opening for material to be shredded, which feeds the material into the path of the rotating blades, and a discharge opening for ejecting shredded debris. However, such an apparatus cannot handle logs or heavy branches.
British Pat. No. 1,303,406 discloses a chipper-shredder comprising a disc-like support plate mounted on a vertical, motor-driven shaft. A chipping blade, with a cutting edge spaced slightly above the disc, is fastened to the top of the disc and extends radially from the shaft. A slot is provided in the disc directly below the cutting edge. Shredding blades are pivotally mounted on pins, extending downward from the disc, around the periphery of the disc. A hopper for the feeding of heavy material to the chipping blade is provided, as well as a hopper for separately feeding light material to the shredding blades. A housing encloses the support plate and associated blades and a tangential discharge opening is provided in the housing. While this machine allows both heavy and light material to be comminuted separately, the radial placement of the chipping blade results in a heavy chopping action which causes excessive wear of bearings supporting the shaft on which the support plate rotates and necessitating a high power, heavy duty motor. Additionally, a spacious blade housing is required to accomodate the shredding blades mounted on the periphery of the support plate. Furthermore, the material shredded can become partly involved in the shredding blades, so that it is only torn into long strips or merely bent about the blade. Such strip-like or bent material tends to catch in the outlet channel and blockages occur necessitating shut-down and cleaning of the machine.
Biersack, U.S. Pat. No. 4,360,166, discloses a motor-driven shredding apparatus for garden waste comprising a cutter housing having a laterally-directed discharge outlet; a cutter support plate mounted within the cutter housing for rotation about a central vertical axis; at least one dependent discharge blade mounted on the lower side of the cutter support plate; at least one radial slot in the cutter support plate with a shredding cutter mounted thereabove; a cylindrical charging container located over the cutter housing, the cutter support plate forming a base for the container, at least one shredding blade mounted centrally on the upper side of the cutter support plate and extending upwardly and outwardly therefrom into the charging container; an inlet for light material at the top of the container; an inlet for heavy material discharging above the cutter support plate; and at least one fixed counter-plate located above the path of rotation of said planar cutting blade and below the path of rotation of said shredding blade. While this patent discloses a compact machine for shredding both heavy and light materials, it utilizes a radially mounted shredding cutter which creates a chopping action. This chopping action places a heavy stress on the shaft supporting the cutter support plate and the bearings supporting that shaft. Moreover, radial positioning and the concommitant chopping action are not very effective in comminuting soft materials such as wet weeds and vines which tend to build up on the blade and may ultimately stop the machine. Comminuted material which falls through the slots can be caught up by the dependent discharge blades and carousel around in the cutter housing beneath the cutter support plate thus blocking discharge of material and ultimately requiring shut-down of the machine for cleaning. The inlet tube for feeding heavy material is set at a rather shallow angle to the cutter support plate and this creates long oval chips which require increased cutting power and further exacerbates the stress due to the chopping action of the shredding cutter. Moreover, this shallow angle also exhibits a tendency to draw parts of the sticks and limbs along the disc travel and never cut them up. The fixed counter plate is angled downwardly so that it forces small twigs and branches onto the cutter plate, however, this tends to cause a build-up of material between the counter-plate and the support plate resulting in a wedge of material acting as a disc brake on the plate and requiring higher motor power. Likewise, twigs fed into the top of the drum are partially broken up and wedged between the inlet tube for heavy material and the support plate resulting in a braking effect. Thus, there is still a need for a machine which does not waste motor power in overcoming unnecessary frictional drag, obtains maximum cutting efficiency and is not subject to clogging.